TOKYO (Reuters) - Toshiba Corp has asked a Japanese law firm to help estimate the potential financial impact if it decides its U.S. nuclear unit Westinghouse should file for Chapter 11 protection from creditors, sources with knowledge of the matter said.

Toshiba is looking at a potential Chapter 11 filing as one of several options for Westinghouse as a means to limit future losses from the Pittsburgh-based company, the two sources said.

The sources declined to be identified as they were not authorized to speak to the media.

Last week, responding to media reports on a potential Chapter 11 filing, Toshiba said it was not aware Westinghouse was considering the step.

A spokesman on Wednesday said the company had no immediate comment on whether a law firm had been approached about the matter.

The TVs-to-construction conglomerate has been plunged into crisis after it emerged that cost overruns at two U.S. nuclear power plant construction projects would result in a $6.3 billion writedown - forcing it to put a majority stake in its prized chips business up for sale.

Analysts and sources with knowledge of the matter have previously said that even under a Chapter 11 filing, Toshiba could still be on the hook for up to $7 billion in contingent liabilities as it has guaranteed Westinghouse’s contractual commitments - an arrangement typical for the nuclear industry.

Toshiba dispatched a group of experts, including lawyers, to Westinghouse in mid-February to assess the U.S. unit’s assets, the two sources said.

Preliminary estimates from that group show a Westinghouse bankruptcy filing would result in Toshiba having to take a fresh charge of at least 300 billion yen ($2.6 billion), the sources said.

That figure is narrower in scope than the $7 billion Toshiba has in contingent liabilities, as it does not include damages that Westinghouse’s customers may seek from Toshiba, including damages that the owners of the two projects could claim if they were not completed.

A Chapter 11 filing would still yield benefits, however, as Westinghouse would come off Toshiba’s consolidated accounts. That could offset some of the charge, the sources said.